The invention relates to a gear shifting device for a multi-speed step-change transmission.
EP O 541 035 discloses a gear shifting device for multi-speed step-change transmissions having valves and shift cylinders in which pistons actuated by a control fluid are located. Shift rods are attached to the shift cylinders which via gear shifting elements act upon parts of the transmission to create a torque-transmitting connection. A shift rod actuates here parts that belong to an auxiliary unit.
The shift rods have great weight which unfavorably contributes to the total weight of the transmission and must be accelerated or decelerated by the gear shifting device upon each gear shifting operation.
The problem on which this invention is based is to disclose a gear shifting device which eliminates the disadvantages of existing gear shifting devices.
It is proposed to provide for each auxiliary unit of a step-change transmission one unit comprising the valves, shift cylinders, pistons and gear shifting elements. Contrary to gear shifting devices known already, this whole gear shifting device sits in the immediate proximity of the auxiliary unit. An auxiliary unit is preferably comprised of two gear wheels disposed side by side in the transmission and can be alternately engaged in the torque transmission. An auxiliary unit, however, can only consist of one engageable gear wheel in the torque transmission when, e.g. two gear wheels opposite each other need not be engaged when shifting to a reverse gear ratio.
By virtue of a compact unit arrangement, it is possible to eliminate connecting elements between the gear shifting elements, preferably formed by shift forks or shift levers, and the shift cylinders and pistons. As already mentioned, such connecting elements are essentially shift rods made of steel which, to a great extent, contribute to the total weight of the transmission. The reaction times between the command that triggers a gear shift and the movement of the gear shifting elements are abbreviated by the elimination of the bulky shift rods to be moved, it is an advantageous development thereby it is possible to use the pulsed 2/2 way valves as triggering valves. It is thus possible, when engaging the gear wheels in a torque-transmitting connection, to adapt shifting force and shifting time. The adaptation preferably consists in the valves being loaded at a higher frequency when engaging than when disengaging the connection. In another advantageous development the pulsed valves are operated with a voltage amounting to a multiple of the standard voltage of the valve. To adapt the pulsed valves, a displacement measuring device is advantageously used, which indicates the actual position of the piston in relation to the shift cylinder. The displacement measuring device is preferably placed within the shift cylinder, but it can also be provided in a position outside the shift cylinder, where it is connected with the movable part of the unit.
In another advantageous development, the piston of the gear shifting unit is situated upon a piston rod, upon which it is axially movable. On the piston rod, it is possible to provide, without hindering each other, the pistons of the gear shifting units of several auxiliary units. The units for each auxiliary unit are preferably disposed in a row.
In another advantageous development, several gear shifting units, of which each gear shifting unit belongs to a respective auxiliary unit, are comprised in one part. The part can be assembled separately from the transmission and then be adapted and attached to the transmission as a unit. This also makes it possible to separately produce and test a complete gear shifting device independent of the type of transmission concerned.